Common Sole Larvae Survive High Levels of Pile-Driving Sound in Controlled Exposure Experiments

In view of the rapid extension of offshore wind farms, there is an urgent need to improve our knowledge on possible adverse effects of underwater sound generated by pile-driving. Mortality and injuries have been observed in fish exposed to loud impulse sounds, but knowledge on the sound levels at which (sub-)lethal effects occur is limited for juvenile and adult fish, and virtually non-existent for fish eggs and larvae. A device was developed in which fish larvae can be exposed to underwater sound. It consists of a rigid-walled cylindrical chamber driven by an electro-dynamical sound projector. Samples of up to 100 larvae can be exposed simultaneously to a homogeneously distributed sound pressure and particle velocity field. Recorded pile-driving sounds could be reproduced accurately in the frequency range between 50 and 1000 Hz, at zero to peak pressure levels up to 210 dB re 1µPa2 (zero to peak pressures up to 32 kPa) and single pulse sound exposure levels up to 186 dB re 1µPa2s. The device was used to examine lethal effects of sound exposure in common sole (Solea solea) larvae. Different developmental stages were exposed to various levels and durations of pile-driving sound. The highest cumulative sound exposure level applied was 206 dB re 1µPa2s, which corresponds to 100 strikes at a distance of 100 m from a typical North Sea pile-driving site. The results showed no statistically significant differences in mortality between exposure and control groups at sound exposure levels which were well above the US interim criteria for non-auditory tissue damage in fish. Although our findings cannot be extrapolated to fish larvae in general, as interspecific differences in vulnerability to sound exposure may occur, they do indicate that previous assumptions and criteria may need to be revised

Effect of pile-driving sounds on the survival of larval fish

Concern exists about the potential effects of pile-driving sounds on fish, but evidence is limited, especially for fish larvae. A device was developed to expose larvae to accurately reproduced pile-driving sounds. Controlled exposure experiments were carried out to examine the lethal effects in common sole larvae. No significant effects were observed at zero-to-peak pressure levels up to 210 dB re 1 μPa 2 and cumulative sound exposure levels up to 206 dB re 1 μPa 2 ·s, which is well above the US interim criteria for nonauditory tissue damage in fish. Experiments are presently being carried out for European sea bass and herring larvae.</p

Effect of pile-driving sounds on the survival of larval fish

Concern exists about the potential effects of pile-driving sounds on fish, but evidence is limited, especially for fish larvae. A device was developed to expose larvae to accurately reproduced pile-driving sounds. Controlled exposure experiments were carried out to examine the lethal effects in common sole larvae. No significant effects were observed at zero-to-peak pressure levels up to 210 dB re 1 μPa 2 and cumulative sound exposure levels up to 206 dB re 1 μPa 2 ·s, which is well above the US interim criteria for nonauditory tissue damage in fish. Experiments are presently being carried out for European sea bass and herring larvae.</p

Comparison of the original and measured signal shape.

<p>Comparison of the original signal shape (recorded in the field) and the observed signal shape (measured in the larvaebrator) for a pressure excitation (A, B) and a velocity excitation (C, D), in terms of sound pressure (A, C) and sound particle velocity (B, D). The original signal is scaled to match the peak of the measured signal. The sound levels are given in the header of each panel.</p

The ‘larvaebrator’ design.

<p>The larvaebrator is a device specifically designed to enable controlled exposure of fish larvae to sound in a laboratory setting.</p

Sound levels of the pressure excitation exposures applied in the pilot experiments.

<p>L_z−p  =  zero to peak sound pressure level, SEL_ss  =  single strike sound exposure level and SEL_cum  =  cumulative sound exposure level, see the text for further explanation. The last 2 columns present the corresponding distance from a ‘typical’ North Sea pile-driving installation and number of strikes.</p

Model estimates of the mean and 95% confidence limits for probability of death in each treatment and for the effect of exposure.

<p>The effect of exposure was defined as 100% • (p_e−p_c)/(1−p_c), in which p_e is the estimated mean probability of death in the exposure group and p_c is the estimated mean probability of death in the control group. The labels of the sound exposure treatments refer to the distance from the pile, the associated sound levels are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033052#pone-0033052-t003" target="_blank">Table 3</a>.</p

Analysis of variance of the probability of death modelled as a function of treatment and random batch effect.

<p>Analysis of variance of the probability of death modelled as a function of treatment and random batch effect.</p